The present invention relates generally to fiber optic cables and, more particularly, to self-supporting fiber optic cables.
Fiber optic cables can be employed in a variety of applications including, for example, the transmission of voice, video and/or data transmission. Fiber optic cables can be installed, for example, in conduits that are disposed within the ground or aerially by being suspended between utility poles. Self-supporting fiber optic cables typically include a messenger section including optical fibers in a tube, and a carrier section including a support member, for example, a steel wire. Self-supporting fiber optic cables should be designed to withstand the relatively large tensile forces that can be experienced during the service life of the cable. In addition, self-supporting fiber optic cables must be capable of withstanding the additional tensile forces associated with thermal effects, wind, and/or ice loading. Self-supporting fiber optic cables should also be capable of withstanding significant vibration.
One type of self-supporting fiber optic cable has a general xe2x80x9cfigure 8xe2x80x9d configuration, wherein the messenger section is connected to the carrier section by at least one web. When the cable is installed, the messenger section bears most of the tension, supporting the carrier section and protecting the optical fibers from the relatively high tensile forces acting on the messenger section. With increasing tension, however, the messenger wire tends to elongate which may cause the carrier section of the cable to elongate. In conventional self-supporting fiber optic cables in which the carrier section has the same length as the messenger section, the elongation of the messenger and carrier sections can place the optical fibers under tension and introduce an undesirable level of optical attenuation. In order to at least partially protect the optical fibers from unnecessarily high tensile forces and/or fiber strain, self-supporting fiber optic cables have been designed to have an overlength of the carrier section with respect to the messenger section. For example, the carrier section can include an overlength of about 0.2% relative to the messenger section. See, for example, U.S. Pat. Nos. 4,662,712 and 4,883,671, the contents of which are incorporated by reference in their respective entireties herein. Messenger section elongation of a self-supporting fiber optic cable that has an overlength can be taken up by the overlength of the carrier section, at least up until the point that the elongation of the messenger section exceeds the overlength of the carrier section. By appropriately designing the self-supporting fiber optic cables such that the overlength of the carrier section is at least as great as the anticipated maximum elongation of the messenger section, the optical fibers can be protected from the relatively high tensile forces acting on the messenger section, thereby controlling optical attenuation. Moreover, the overlength can be advantageous for mid-span access of the optical fibers.
Self-supporting fiber optic cables are conventionally designed such that the overlength of the carrier section can xe2x80x9csagxe2x80x9d in almost any direction. For example, the self-supporting fiber optic cables described by U.S. Pat. Nos. 4,662,712 and 4,883,671 exhibit uncontrolled sagging between web-like supports relative to the messenger section. The possibility that the carrier section may be disposed in almost any direction relative to the messenger section can be disadvantageous with respect to the packaging and shipping of the fiber optic cable. Fiber optic cables are typically wound upon a reel for shipment prior to installation. Since the carrier section may not always be disposed in the same manner relative to the messenger section, and the spacing between the messenger and carrier sections may vary, the fiber optic cable cannot generally be wound onto the reel in a uniform fashion. Moreover, the strength members in the wound cable can be dislodged during the winding step because the radially outermost strength member could be under significant tension and can move toward the center of the cable and may partially or catastrophically crush the tube. Alternatively, significantly tensioned strength members may slip circumferentially about the tube.
The present invention can be practiced in the form of a fiber optic cable comprising: a messenger section comprising at least one support member; a jacket surrounding the at least one support member; a carrier section having an over-length with respect to the messenger section, the carrier section comprising a tube, at least one optical fiber disposed within the tube, at least one strength member proximate the tube; a jacket surrounding the tube and the at least one strength member, and a plurality of intermittent webs connecting the respective jackets of the messenger section and the carrier section.
The present invention can also be practiced in the form of a fiber optic cable comprising: a messenger section comprising at least one support member and a jacket surrounding the at least one support member; a carrier section comprising a tube having at least one optical fiber disposed within the tube; at least one strength member positioned proximate the tube; and a jacket surrounding the tube and the at least one strength member, a web connecting the respective jackets of the carrier section and the messenger section, the at least one strength member being generally positioned in a reference plane that also generally extends through the messenger section, the carrier section and the web thereby imparting a preferential bend characteristic to the fiber optic cable.
The present invention can be practiced in the form of a fiber optic cable comprising: a messenger section comprising at least one support member and a jacket surrounding the at least one support member; a carrier section having an over-length with respect to the messenger section, the carrier section comprising a tube with at least one optical fiber disposed within the tube; a jacket surrounding the tube and the at least one strength member; and a plurality of intermittent webs connecting the respective jackets of the messenger section and the carrier section; the at least one strength member and the messenger section imparting a preferential bend characteristic to the cable whereby the carrier section preferentially bends in a plane generally orthogonally disposed to a reference plane that generally extends through the messenger section, the carrier section and the web.